Trailing edges of nozzle vanes in gas turbines often contain cooling passages for cooling the trailing edges. Typically, cooling air is provided in a cavity in the vane and passes through a plurality of passages spaced from one another along the length of the trailing edge of the vane and exits into the hot gas path. The cooling air cools the metal of the trailing edge surrounding the passages and along outer surfaces of the trailing edge. Conventionally, thermal barrier coatings are provided along the side walls of the trailing edge and about the trailing edge tip. However, notwithstanding efforts to uniformly apply the thermal barrier coating to the side walls and tip of the trailing edge, the coating oftentimes breaks off from the tip during handling or spalls off the tip during operation. Thus, cooling the tip of the trailing edge is of particular concern and therefore requires heat transfer enhancement for effective cooling.
Turbulators have also been employed in the passages for cooling the trailing edges of nozzles. The turbulators interrupt the cooling air flow, creating turbulence and cause enhanced cooling effect. Turbulators are conventionally located along the entire length of the cooling passages. This therefore results in enhanced cooling of the surrounding metal and trailing edge surfaces throughout the length of the trailing edge passages. The material of these regions, however, are protected, to a large extent, by the thermal barrier coating along the sides of the trailing edge. Consequently, the region requiring cooling enhancement, i.e., the tip of the trailing edge, is effectively cooled, while those regions which are protected by the thermal barrier coating and do not require cooling enhancement are nonetheless provided with enhanced cooling effects by the turbulators. This causes a wide-ranging temperature distribution laterally along the trailing edge, with consequent thermal mismatches resulting in high stresses in the metal of the trailing edge.
Further, it will be appreciated that air for cooling the trailing edge of nozzle vanes typically comprises compressor discharge air. To the extent air is bled from the compressor for cooling purposes, the turbine has diminished efficiency. Accordingly, the problem at hand is to provide enhanced cooling effect in the regions requiring enhanced cooling, while eliminating enhanced cooling for those regions of the trailing edge which do not require enhanced cooling, while simultaneously limiting required cooling bleed air from the compressor discharge.